AP Biology Unit 2 Practice Questions: Cell Structure and Function MCQs and FRQs

A red blood cell is placed in a solution with a higher solute concentration than the cytoplasm. What will most likely happen to the cell?

1. A. Water leaves the cell and it shrinks (crenates)
2. B. Solute diffuses into the cell until concentrations equalize with no water movement
3. C. Water enters the cell and it swells and may lyse
4. D. The cell remains unchanged because the membrane blocks all osmosis

A plant cell is placed in distilled water. Which outcome best describes the cell after osmosis?

1. A. The cell plasmolyzes because water leaves toward the hypotonic surroundings
2. B. No net water movement occurs because the cell wall is impermeable to water
3. C. The cell becomes turgid as water enters and presses the vacuole against the cell wall
4. D. The cell wall ruptures immediately because plant membranes cannot regulate water

Water moves from an area of higher water potential to an area of lower water potential. In an open beaker at room temperature, pure water has:

1. A. The highest water potential in the system
2. B. Lower water potential than a concentrated salt solution
3. C. Zero water potential only when solute is added
4. D. Water potential determined solely by pressure, not solute concentration

Aquaporins in the plasma membrane primarily increase the rate of:

1. A. Active transport of glucose against its gradient
2. B. ATP synthesis in the mitochondrial matrix
3. C. Water diffusion across the lipid bilayer
4. D. Bulk flow of proteins through endocytosis

Two solutions, A and B, have equal molar concentrations of NaCl. Solution A also contains a membrane-impermeant starch polymer that cannot cross the cell membrane. A cell permeable only to water is placed in each solution separately. Which statement is correct?

1. A. The cell shrinks in A but not in B because A has lower water potential despite equal NaCl
2. B. The cell crenates in B because starch lowers water potential in the external solution
3. C. The cell behaves the same in A and B because only NaCl affects tonicity
4. D. The cell swells in both solutions because NaCl concentrations are identical

Which pairing best illustrates the principle that structure supports function in cells?

1. A. Ribosomes package proteins into vesicles for secretion
2. B. The nucleus produces ATP for cellular work
3. C. Microvilli increase surface area for absorption in intestinal epithelial cells
4. D. Lysosomes store genetic information for protein synthesis

As a hypothetical cell doubles in diameter, which change creates the greatest challenge for maintaining efficient exchange with the environment?

1. A. Volume increases eightfold while surface area increases only fourfold
2. B. Surface area decreases while volume stays constant
3. C. Surface area increases eightfold while volume increases only fourfold
4. D. Both surface area and volume increase by the same factor

Which cellular feature is most directly involved in maintaining homeostasis by controlling what enters and leaves the cell?

1. A. Free-floating DNA in the cytosol of eukaryotes
2. B. Selectively permeable plasma membrane
3. C. Central vacuole in all animal cells
4. D. Cell wall in mammalian red blood cells

Ribosomes are the site of:

1. A. Translation of mRNA into polypeptide chains
2. B. Replication of nuclear DNA before mitosis
3. C. Hydrolysis of macromolecules in acidic vesicles
4. D. Light-dependent reactions of photosynthesis

A protein destined for secretion follows which pathway order in a typical animal cell?

1. A. Golgi apparatus → rough ER → lysosome → nucleus
2. B. Smooth ER → ribosome → nucleolus → cytoplasm only
3. C. Rough ER → Golgi apparatus → secretory vesicle → plasma membrane
4. D. Free ribosome → mitochondrion → chloroplast → cell wall

Which organelle is the primary site of ATP production through aerobic cellular respiration in eukaryotic cells?

1. A. Mitochondrion
2. B. Peroxisome
3. C. Chloroplast
4. D. Smooth endoplasmic reticulum

Chloroplasts are found in plant cells and are best described as:

1. A. Organelles that digest worn organelles using hydrolytic enzymes
2. B. Sites of protein secretion with bound ribosomes on outer membrane
3. C. Sites of photosynthesis with internal thylakoid membranes
4. D. Structures that assemble ribosomal subunits from rRNA

Lysosomes contribute to cellular recycling primarily by:

1. A. Generating ATP through substrate-level phosphorylation
2. B. Synthesizing lipids for the plasma membrane
3. C. Storing hereditary information as circular DNA
4. D. Breaking down macromolecules and damaged organelles with hydrolytic enzymes

Which observation would most strongly indicate that a cell is eukaryotic rather than prokaryotic?

1. A. A membrane-bound nucleus containing chromatin
2. B. Circular DNA located in the nucleoid region
3. C. A plasma membrane composed of a phospholipid bilayer
4. D. Presence of ribosomes in the cytoplasm

Ribosomes are found in both prokaryotic and eukaryotic cells because:

1. A. All cells perform photosynthesis in chloroplasts
2. B. All living cells must synthesize proteins
3. C. Both cell types store DNA in a membrane-bound nucleus
4. D. Both rely on mitochondria for ATP production

Which statement correctly describes typical bacterial cells?

1. A. They are eukaryotic, contain mitochondria, and are always larger than plant cells
2. B. They are prokaryotic, lack a nucleus, and are generally smaller than eukaryotic cells
3. C. They have membrane-bound Golgi apparatus but no ribosomes
4. D. They store DNA only inside chloroplasts

A student views an unknown cell and sees mitochondria, a Golgi apparatus, and endoplasmic reticulum. This cell most likely:

1. A. Is acellular because it lacks a plasma membrane
2. B. Is prokaryotic because all cells contain ER
3. C. Is eukaryotic because these are membrane-bound organelles
4. D. Is a bacterium because it has internal membrane systems

A cube-shaped cell has sides of 2 μm. What is its surface-area-to-volume ratio?

1. A. 3 μm⁻¹
2. B. 1.5 μm⁻¹
3. C. 2 μm⁻¹
4. D. 4 μm⁻¹

Why are most efficient exchange surfaces found in smaller cells or specialized projections?

1. A. Smaller cells have a higher surface-area-to-volume ratio
2. B. Larger cells always have more membrane channels per square micrometer
3. C. Volume decreases faster than surface area as cells grow
4. D. Smaller cells have lower metabolic demand and no need for transport

When a cell grows uniformly so each linear dimension triples, which statement about scaling is correct?

1. A. Surface area and volume both increase 3-fold
2. B. Volume increases 9-fold while surface area increases 27-fold
3. C. Volume increases 27-fold while surface area increases 9-fold
4. D. Surface area decreases because the membrane stretches thinner

Microvilli in the small intestine primarily function to:

1. A. Decrease surface area to reduce water loss
2. B. Generate ATP through oxidative phosphorylation
3. C. Store genetic material separate from the nucleus
4. D. Increase apical surface area for nutrient absorption

The basic structural framework of the plasma membrane is the:

1. A. Phospholipid bilayer
2. B. Cellulose matrix
3. C. Actin filament network
4. D. Peptidoglycan wall

In a phospholipid bilayer, the hydrophilic heads and hydrophobic tails are oriented so that:

1. A. Heads and tails randomly flip every few seconds with no stable orientation
2. B. Tails dissolve in water while heads cluster in the membrane center
3. C. Tails contact cytoplasm and heads face the nonpolar interior
4. D. Heads contact aqueous fluids on both sides and tails face each other inside the membrane

The fluid mosaic model describes the plasma membrane as:

1. A. A single layer of phospholipids with cholesterol on the exterior only
2. B. A dynamic bilayer with proteins that can move laterally among phospholipids
3. C. A static crystal lattice that prevents any molecular motion
4. D. A rigid sheet of proteins with no lipid component

Cholesterol in animal cell membranes helps maintain fluidity by:

1. A. Replacing all phospholipids so the membrane becomes purely protein
2. B. Preventing fatty acid tails from packing too tightly at low temperature and restraining excessive movement at high temperature
3. C. Converting the bilayer into a cell wall
4. D. Blocking all transport proteins from functioning

Oxygen (O₂) crosses the plasma membrane easily primarily because it is:

1. A. Small and nonpolar, so it diffuses through the hydrophobic interior
2. B. A protein that binds receptor sites on the outer leaflet
3. C. Large and charged, so it uses voltage-gated channels
4. D. Polar and always requires ATP-powered pumps

Sodium ions (Na⁺) generally cannot cross the plasma membrane unaided because:

1. A. The hydrophobic interior repels charged particles and they require channel or pump proteins
2. B. Na⁺ is too large to fit through any protein and therefore never enters cells
3. C. They are nonpolar and dissolve in the lipid core faster than water
4. D. The membrane is fully permeable to all ions by simple diffusion

Glucose uptake into many animal cells often requires a carrier protein because glucose is:

1. A. A nonpolar gas that moves only by osmosis
2. B. Always moved against its gradient without any protein assistance
3. C. Identical to oxygen in membrane permeability
4. D. A large polar molecule that cannot diffuse freely through the lipid bilayer

Although water is polar, it crosses membranes rapidly when aquaporins are present because:

1. A. Aquaporins provide selective channels that speed water movement
2. B. Water only moves by active transport using ATP
3. C. Aquaporins convert water into nonpolar molecules
4. D. Aquaporins hydrolyze water into ions before transport

Simple diffusion moves molecules:

1. A. From regions of higher concentration to regions of lower concentration
2. B. Only when a membrane protein hydrolyzes GTP
3. C. From lower concentration to higher concentration using ATP
4. D. Against the electrochemical gradient until ATP is depleted

Facilitated diffusion differs from active transport because facilitated diffusion:

1. A. Uses transport proteins but does not require ATP to move solutes down their gradient
2. B. Always moves substances against their concentration gradient
3. C. Requires hydrolysis of ATP for each molecule transported
4. D. Only occurs for nonpolar gases and never uses proteins

At diffusion equilibrium for a solute across a permeable membrane:

1. A. The solute concentration is always zero on both sides
2. B. There is no net movement even though individual molecules still cross the membrane
3. C. All molecular movement stops completely
4. D. ATP must continuously power equal flux in both directions

A student claims that because the Na⁺/K⁺ pump uses a transport protein, it must be facilitated diffusion. Which response best refutes the claim?

1. A. The pump moves Na⁺ and K⁺ down their gradients without energy input
2. B. All transport proteins work only by passive diffusion regardless of energy use
3. C. Facilitated diffusion always requires ATP hydrolysis per molecule
4. D. The pump moves ions against their electrochemical gradients using ATP, which is active transport

Active transport is defined as movement of substances:

1. A. Against their concentration or electrochemical gradient using energy
2. B. Only of water through aquaporins by osmosis
3. C. Down a concentration gradient without any proteins
4. D. Exclusively of lipids through the bilayer interior

For each ATP hydrolyzed, the sodium-potassium pump typically moves:

1. A. Na⁺ and K⁺ only by facilitated diffusion with no ATP
2. B. 1 Na⁺ and 1 K⁺ in the same direction out of the cell
3. C. 2 Na⁺ out and 3 K⁺ in
4. D. 3 Na⁺ out of the cell and 2 K⁺ into the cell

A proton pump in the membrane of plant root cells contributes to nutrient uptake by:

1. A. Using ATP to move H⁺ out, creating a gradient that drives cotransport of ions and solutes
2. B. Hydrolyzing starch in the cell wall
3. C. Allowing protons to diffuse down their gradient without proteins
4. D. Blocking all active transport across the plasma membrane

Which process moves large particles or bulk amounts of material across the plasma membrane using vesicles?

1. A. Simple diffusion of oxygen
2. B. Osmosis through aquaporins only
3. C. Endocytosis and exocytosis
4. D. Passive facilitated diffusion of glucose

Compartmentalization in eukaryotic cells increases metabolic efficiency mainly by:

1. A. Separating incompatible reactions and concentrating enzymes and substrates in specific organelles
2. B. Preventing proteins from ever crossing membranes
3. C. Eliminating the need for any membrane transport
4. D. Making all enzymes function at identical pH in the cytosol

A newly synthesized secretory protein is sorted through compartmentalized organelles. Which sequence reflects correct shipping?

1. A. Rough ER lumen → Golgi modification → transport vesicle → plasma membrane fusion
2. B. Golgi → free ribosome → peroxisome → nucleoid
3. C. Cytosol → nucleus → chloroplast → cell wall deposition
4. D. Mitochondrial matrix → lysosome → ribosome → smooth ER

A nerve cell maintains a high internal K⁺ concentration and low Na⁺ concentration. After treatment with a drug that inhibits the Na⁺/K⁺ pump but leaves channel proteins functional, which outcome is most likely over time?

1. A. The membrane becomes impermeable to all ions immediately
2. B. Na⁺ is actively pumped in and K⁺ out faster than before
3. C. Na⁺ and K⁺ gradients dissipate as ions leak through channels down their electrochemical gradients
4. D. Water stops moving and the cell becomes hypertonic to its environment without any volume change